Rubber composition

ABSTRACT

A brominated butyl rubber and a polymer based on a conjugated diolefin monomer are grafted by mixing the solid polymer at a temperature greater than 50° C. for a time sufficient to cause grafting. The grafted copolymer is useful especially in tire tread compositions.

FIELD OF THE INVENTION

This invention relates to a process for the grafting on to brominatedbutyl rubbers of polymers based on conjugated diolefin monomers and theuse of these graft copolymers in rubber compositions that, uponvulcanization, exhibit improved physical properties. The graftcopolymers are particularly, but not exclusively, suited for use in tiretread compositions.

BACKGROUND OF THE INVENTION

With the increasing demand for automobile safety and low fuelcomsumption, specifications for rubber compounds for tire treads havebecome more demanding. Tire treads are required to be very tough andvery wear resistant, to have a high degree of traction on both wet anddry surfaces, to provide low rolling resistance and heat build up and toretain their rubbery characteristics over a wide temperature range.However, some of these requirements are essentially incompatible withother requirements.

The addition of a butyl rubber to the tread formulation of a tire leadsto an improvement in the wet skid resistance of the tire tread but thereis a concomitant reduction in the wear resistance of the tire tread.Thus it would be desirable if the butyl rubber could be modified in amanner such that, when used in a tire tread formulation, the improvedwet skid resistance is retained and, additionally, there is improvedwear resistance while a desirable balance of the other physicalproperties is maintained.

As butyl rubbers have a very low level of unsaturation they do not havegood compatibility with highly unsaturated rubbers such as polybutadieneor styrene-butadiene copolymers. Consequently several different graftingprocedures have been developed by means of which further unsaturationmay be introduced.

U.S. Pat. No. 5,264,494 discloses one process for preparing graftcopolymers of halogenated butyl rubbers and polymers based on conjugateddiolefin monomers. This process involves use of a solution of achlorinated butyl rubber or a brominated butyl rubber, in a inertsolvent, and a solution of a living, alkali metal terminated polymerbased on conjugated diolefin monomers. This process is expensive anddisadvantageous, as the living polymer is extremely sensitive tomoisture and to impurities, so extreme precautions must be taken toprotect it, the reaction mixture containing it and the halogenated butylrubber, from moisture and impurities. Hence, the inert organic solventor solvents must be moisture-free, and the reaction must be carried outunder an inert atmosphere, for instance under nitrogen. Furthermore,ensuring that the polymers to be grafted are not contaminated withimpurities can involve several washing steps, and the solvent orsolvents must be removed from these washing steps and from the productafter the reaction. For environmental reasons, it is desirable to avoiduse of large volumes of organic solvents where possible.

U.S. Pat. No. 5,342,896 also relates to the preparation to graftcopolymers composed of a halobutyl rubber and a polymer based on a dienemonomer. This process uses a lithium-terminated diene-capped vinylaromatic polymer that is reacted with the halobutyl rubber. Thelithium-terminated diene-capped vinyl aromatic polymer can be preparedby adding a small amount of diene monomer to a solution of livinglithium-terminated polystyrene. This reaction is carried out in an inertorganic solvent such as cyclohexane and under an inert atmosphere.Again, precautions against moisture and impurities must be taken, inview of the moisture sensitivity and sensitivity to impurities of theliving polymer and, again, organic solvents are used.

The present invention provides a process for preparing graft copolymersof brominated butyl rubbers and polymers based on conjugated diolefinmonomers that does not involve use of living polymers and, therefore,avoids the disadvantages that accompany their use. It also avoids use oforganic solvent in the formation of the graft copolymer.

SUMMARY OF THE INVENTION

The present invention provides a process for preparing a graft copolymerof a brominated butyl rubber and a polymer based on a conjugateddiolefin monomer, which process comprises mixing a solid brominatedbutyl rubber with a solid polymer which is based on a conjugateddiolefin monomer and which also includes some C—S—(S)_(n)—C bonds, wheren is an integer from 1 to 7, the mixing being carried out at atemperature greater than 50° C., for a period of time sufficient tocause grafting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the Stress versus Strain of Graft of Blend RubbersVulcanisates.

FIG. 2 illustrates the Stress versus Strain of Graft of Blends filledwith Carbon Black.

FIG. 3 illustrates the tan (δ) versus temperature for a 50/50 blend of abrominated butyl rubber and sulphurised polymer based on conjugateddiolefin monomers and for 50/50 grafts of POLYSAR BB2040 with BUNA CB24and BUNA 25.

FIG. 4 illustrates the tan (δ) versus temperature for a 70/30 blend ofBUNACB25 and POLYSAR BB2040 and a 70/30 graft of BUNA CB25 and POLYSARBB2040 formed by mixing in a Banbury mixer for 16 minutes with a dumptemperature of 150° C.

FIG. 5 illustrates the tan (δ) versus temperature for a 30/70 blend ofBUNA CB25 and POLYSAR BB2040 and a 70130 graft of BUNA CB25 and POLYSARBB2040 formed by mixing in a Banbury mixer for 17 minutes with a dumptemperature of 143° C.

DETAILED DESCRIPTION OF THE INVENTION

It is necessary that the two polymers, the brominated rubber and thediene-based polymer, shall be mixed in a manner that ensures gooddispersion within each other to ensure reaction between the reactivegroups of the two polymers. Conditions that ensure the requireddispersion occur in internal mixers such as Banbury mixers, and Haakeand Brabender miniature internal mixers. A two roll mill mixer alsoprovides good dispersion of one polymer within another. An extruderprovides good mixing and permits a shorter reaction time. It is possibleto carry out the mixing in two or more stages, and the mixing can bedone in different apparatus, for example one stage in an internal mixerand one stage in an extruder.

The temperature of the mixed polymers is important, and should begreater than 50° C., preferably greater than 60° C., to ensure that thegrafting reaction occurs to a significant extent. At high temperaturesthere may occur significant deterioration of the polymers in the form ofcrosslinking, causing gelation, or chain scission, and the mixing shouldbe done at a temperature that does not cause this deterioration tooccur. For this reason the temperature should not normally exceed 180°C. A temperature in the range from 60° to 160° C. is preferred and atemperature in the range from 80° to 140° C. is particularly preferred.Deterioration is worsened if a high temperature is maintained for a longperiod of time; the lower the temperature, the longer the polymers canbe mixed.

When using mill rollers to mix the polymers to form the graft, thetemperature of the mill rollers can be set, and mixing commenced. Asmixing proceeds the temperature of the polymer mixture is measured, andthis may be quite different from the temperature of the mill rollers.When reference is made to the temperature at which mixing is proceeding,it is the temperature of the polymer mixture that is being referred to.

The time period over which mixing is carried out can vary over widelimits. The time required for mixing varies with the extent of mixing.If mixing is done in an extruder the mixing is more efficient than ifdone in a mixer, and hence less time is required. The time may be aslittle as one minute or may be two hours or more. More often it isbetween 1 and 20 minutes. The fact that grafting has occurred can bedemonstrated by means of a simple test. Brominated butyl rubbers andpolymers based on conjugated diolefin monomers can be dissolved inhexane to achieve a solution of 5 g rubber, or 5 g polymer, in 100 ghexane. If an ungrafted mixture of brominated butyl rubber and polymerof conjugated diolefin is dissolved in hexane and left to stand at roomtemperature there occurs separation into two phases, within two or threehours, as the brominated butyl rubber remains in solution but thepolymer of conjugated diolefin precipitates out. In contrast, if thebrominated butyl rubber and polymer of conjugated diolefin have beenmixed at a temperature above 50° C., to cause grafting, and the productof the mixing is dissolved in hexane, little or no settling occurs overseveral days, indicating that a large part, or all, of the brominatedbutyl rubber and polymer of conjugated diene have grafted. Anotherindication that grafting has occurred is that the glass transitiontemperature, Tg, of the grafted copolymer is shifted, as compared withthe Tg of the ungrafted bromobutyl rubber and the Tg of the polymerbased on the conjugated diolefin.

It is possible to carry out a pre-mixing step, at a temperature below50° C., before the polymeric mixture is subjected to mixing at atemperature above 50° C. to cause grafting.

The brominated butyl rubbers suitable for use in this invention areobtained by bromination of butyl rubber, which is a copolymer ofisobutylene and a comonomer that is usually a C4 to C6 conjugateddiolefin, preferably isoprene. Comonomers other than conjugateddiolefins can be used, however, and mention is made of alkyl-substitutedvinyl aromatic comonomers such as C₁-C₄-alkyl substituted styrene. Oneexample that is commercially available is brominated isobutylenemethylstyrene copolymer (BIMS) in which the comonomer isp-methylstyrene.

Brominated butyl rubber typically contains in the range of from 1 to 3weight percent of isoprene and in the range of from 97 to 99 weightpercent of isobutylene based on the hydrocarbon content of the polymers,and in the range of from 1 to 4 weight percent bromine based on thebromobutyl polymer. A typical bromobutyl polymers has a molecularweight, expressed as the Mooney (ML 1+8 at 125° C.) according to DIN 53523, of in the range of 28 to 55.

In the process of the present invention the brominated butyl rubberpreferably contains in the range of from 1 to 2 weight percent ofisoprene and in the range of from 98 to 99 weight percent of isobutylenebased on the hydrocarbon content of the polymer and in the range of from0.5 to 2.5 weight percent, preferably in the range of from 0.75 to 2.3weight percent, of bromine based on the brominated butyl polymer.

A stabilizer may be added to the brominated butyl rubber. Suitablestabilizers include calcium stearate and epoxidized soyabean oil,preferably used in an amount of in the range of from 0.5 to 5 parts byweight per 100 parts by weight of the brominated butyl rubber.

Potentially any polymer containing carbon-carbon double bonds can besulphurised, for example by reaction with S₂Cl₂, and then grafted withthe brominated butyl rubber, and mention is made of polymers andcopolymers of conjugated diolefins. Such conjugated diolefin polymersand copolymers can be prepared using a number of different catalystsystems. Mention is made of anionic systems, systems based on transitionmetals, systems based on lanthanide metals, for example neodymium, andfree radical systems. The conjugated diolefins generally have thestructural formula:

R—CN═C(R₁)—C(R₁₁)═CH₂

wherein R is a hydrogen atom or an alkyl group containing from 1 to 8carbon atoms and wherein R₁ and R₁₁ can be the same or different and areselected from the group consisting of hydrogen atoms and alkyl groupscontaining from 1 to 4 carbon atoms. Some representative nonlimitingexamples of suitable conjugated diolefins include 1,3-butadiene,isoprene, 2-methyl-1,3-pentadiene, 4-butyl-1,3-pentadiene,2,3-dimethyl-1,3-pentadiene 1,3-hexadiene, 1,3-octadiene,2,3-dibutyl-1,3-pentadiene, 2-ethyl-1,3-pentadiene,2-ethyl-1,3-butadiene and the like. Conjugated diolefin monomerscontaining from 4 to 8 carbon atoms are preferred, 1,3-butadiene andisoprene being especially preferred.

The polymer based on a conjugated diene monomer can be a homopolymer, ora copolymer of two or more conjugated diene monomers, or a copolymerwith a vinyl aromatic monomer.

The vinyl aromatic monomers which can optionally be used are selected soas to be copolymerizable with the conjugated diolefin monomers beingemployed. Generally, any vinyl aromatic monomer which is known topolymerize with organo alkali metal initiators can be used. Such vinylaromatic monomers usually contain from 8 to 20 carbon atoms, preferablyfrom 8 to 14 carbon atoms. Some examples of vinyl aromatic monomers thatcan be copolymerized include styrene, alpha-methyl styrene, variousalkyl styrenes, p-methoxy styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, 4-vinyl toluene and the like. Styrene is preferred forcopolymerization with 1,3-butadiene alone or for terpolymerization withboth 1,3-butadiene and isoprene.

Preferred polymers based on conjugated diolefin monomers, for graftingonto the brominated butyl rubber, are selected from the group consistingof butadiene rubbers, styrene-butadiene random and block rubberycopolymers and styrene-isoprene-butadiene rubber and mixtures thereof,preferably from the group consisting of butadiene rubbers,styrene-butadiene random copolymers and mixtures thereof, and morepreferably from butadiene rubbers.

The relative amount of conjugated diolefin monomers and vinyl aromaticmonomers employed can vary over a wide range. However, in general atleast 50 mole percent conjugated diolefin monomers are required in orderto produce a rubbery copolymer. Thus the mole ratio of conjugateddiolefin monomers to vinyl aromatic monomers will be in the range of50:50 to 99:1. More typically the mole ratio of conjugated diolefinmonomers to vinyl aromatic monomers will be in the range of 65:35 to95:5.

The vinyl content in the conjugated diolefin portion of the polymerchain may be controlled by the use of a microstructure controlling agentsuch as an ether or a tertiary amine. Representative nonlimitingexamples of ethers that may be used as microstructure controlling agentsinclude dioxane, tetrahydrofuran and derivatives thereof, ethyleneglycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycoldimethyl ether, diethylene glycol diethyl ether, triethylene glycoldimethyl ether and derivatives thereof or the like.

Representative nonlimiting examples of tertiary amines includetriethylamine, N,N,N′,N′-tetramethylethylene-diamine and the like. Theamount of the microstructure controlling agent varies depending upon themicrostructure of the desired conjugated diolefin containing polymer orthe conjugated diolefin-vinyl substituted aromatic monomer copolymer andit is in the range of from 0.05 to 2,000 moles, preferably 0.2 to 1,000moles per mole of organometallic catalyst.

The polymerization process can be carried out at any temperature withinthe range of −80° C., to 150° C. but preferably the polymerizationprocess is carried out at a temperature of in the range of −20° C., to80° C.

The polymer based on conjugated diolefin monomers contains C—S—(S)_(n)—Cbonds, where n is an integer from 1 to 7 and the free valence bond maybe satisfied by any of several atoms, including carbon, hydrogen ornitrogen. These bonds can be introduced, for instance, by reacting apolymer based on conjugated diolefin monomers with a sulphurising agent,for instance sulphur dibromide or, preferably, sulphur dichloride,S₂Cl₂, resulting in the formation of C—S—(S)_(n)—C bonds betweenpolymeric chains. It is believed that when the diolefin is butadiene andthe sulphurising agent is sulfur dichloride the structure connecting thechains is as follows:

If the sulphurising agent is sulphur dichloride or sulphur dibromide,then n usually takes the value of 1. Other sulfurising agents, forexample sulphur, S_(n), result in higher values of n up to 7. See, forexample, Organic Sulphur Compounds, edited by M. Kharasch, PergamonPress, pages 210 and 211, incorporated herein by reference.

The polymer based on the conjugated diene generally contains from 0.001to 5 weight percent of sulphur based on the weight of the polymer,preferably from 0.01 to 1 weight percent.

The sulphurising agent can be reacted with the polymer by addition ofthe sulphurising agent, preferably sulphur dichloride, to the finalstage of the polymerization reaction by which the polymer is formed, orby reacting the polymer with sulphur dichloride after the polymerizationreaction has been completed. Two sulphur containing polybutadienes arecommercially available from Bayer under the trade marks BUNA CB24 andBUNA CB25.

The weight ratio of the brominated butyl rubber to the polymer based onconjugated diolefin monomers can vary between wide limits and issuitably in the range from 90:10 to 10:90 preferably from 70:30 to30:70. For many purposes a 50:50 ratio is suitable.

On completion of the reaction suitable antioxidants may be added to thegraft copolymer. Suitable antioxidants include sterically hinderedphenols, preferably used in the amount of in the range of 0.005 to 2parts by weight per 100 parts by weight of the graft copolymer.

The graft-polymer itself, a rubber composition containing saidgraft-polymer, a vulcanized rubber composition containing saidgraft-polymer and a rubber article made of said rubber compositioncontaining said graft-polymer are further objects of the invention.

The disclosed graft polymers can be compounded with at least one rubberypolymer selected from the group consisting of butadiene rubbers,styrene-butadiene random and block copolymers andstyrene-isoprene-butadiene random and block copolymers andstyrene-isoprene-butadiene rubber, and with carbon black andvulcanization agents. Preferably in the range of from 10 to 90 parts byweight of the graft copolymer are compounded with in the range of from90 to 10 parts by weight of at least one rubbery polymer for a total of100 parts by weight of the total of the graft copolymer and rubberypolymers. More preferably, in the range of from 10 to 50 parts by weightof the graft copolymer are compounded with in the range of from 90 to 50parts by weight of rubbery polymer.

The rubber compositions further comprise natural rubber and/or syntheticrubbery polymers based upon conjugated diolefinic monomers which arecompatible and covulcanizable with the aforesaid graft copolymer.Preferably in the range of from 10 to 90 parts by weight of at least onerubbery polymer selected from the group consisting of butadiene rubbers,styrene-butadiene random and block rubbery copolymers, isoprene rubberand natural rubber are mixed with in the range of from 90 to 10 parts byweight of the graft copolymer for a total of 100 parts by weight of thepolymers. More preferably, in the range of from 50 to 90 parts ofrubbery polymer are mixed with in the range of from 50 to 10 parts ofgraft copolymer.

The use of carbon blacks for reinforcement of vulcanizates is well knownin the art and results in improved strength properties of the finalvulcanizates. Suitable carbon blacks for practicing this inventioninclude the well known furnace and channel, preferably furnace, blacksand are used in amounts of in the range of from 30 to 150 parts byweight per 100 parts of rubber. Other suitable fillers include silica,clays, and mixtures of silica and carbon black.

The curing system suitable for use in the present invention is notparticularly restricted. A typical curing system comprises: (i) a metaloxide; (ii) optionally, elemental sulphur and (iii) at least one sulphurbased accelerator. The use of metal oxides as a curing component is wellknown in the art. A suitable metal oxide is zinc oxide, which may beused in amounts of in the range of from 1 to 10, preferably from 2 to 5,parts by weight. Elemental sulphur, comprising component (ii) of saidcuring system, when present, may be used in amounts of in the range offrom 0.2 to 2 parts by weight. Suitable sulphur accelerators (component(iii) of said curing system) may be used in amounts of in the range offrom 0.5 to 3 parts by weight and include the thiuram sulphides such astetramethyl thiuram disulphide (TMTD), the thiocarbamates such as zincdimethyl dithiocarbamate (ZDC) and the sulfenamides such asN-cyclohexyl-2-benzothiazol sulfenamide. Preferably the sulphur basedaccelerator is N-cyclohexyl-2-benzo-thiazole sulfenamide.

Stabilizers, anti-oxidants, hydrocarbon extender oils and tackifiers mayalso be added as is well known in the art of compounding.

The compositions containing the graft copolymer according to the presentinvention, together with the further natural rubber or synthetic rubberypolymer can be prepared by the well known methods for mixing rubberypolymers including mixing on a rubber mill or in internal mixers of theBanbury or Brabender variety. Generally it is preferred to carry out thecompounding procedure in two stages. In the first stage the polymers maybe mixed with conventional compounding ingredients; these may includecarbon black, hydrocarbon extender oil, tackifiers, stabilizers,processing acids and antioxidants. In the second stage of thecompounding procedure, the cure active agents are preferably added tothe compound described above on a rubber mill or in an internal mixeroperated at a temperature not normally in excess of 60° C. The compoundsare cured in a conventional manner by heating in the range of from 5 to60 minutes at temperatures in the range of from 150° C. to 200° C. toform elastomeric vulcanizates.

After vulcanization, the rubber compositions hereinbefore describedexhibit an improved balance of physical properties. By physicalproperties is meant hardness and elongation and strength propertieswhich include modulus at 100 percent elongation, modulus at 300 percentelongation and tensile strength at rupture.

As stated above, the graft polymers themselves or compositionscontaining said graft polymers or vulcanized compositions containingsaid graft polymers are partially suited for use in tire treadcompositions. They are also useful, however, for manufacturing all kindof articles, especially belts such as conveyer belts, and rolls. Theydisplay good damping properties and are, therefore, also useful inisolators against vibration and in mounts and bushings.

The following examples illustrate the present invention and are notintended to limit the scope thereof. All parts are parts by weightunless otherwise specified. The accompanying drawings are graphs showingproperties of the grafts of the invention.

In the examples use is made of the polymers described below: POLYSAR®BB2040 (POLYSAR is a registered trademark of Bayer Ag.) is a brominatedbutyl nibber that is available from Bayer. It has a Mooney viscosity(RPML 1+8 @ 125° C.) of 39±4, a bromine content of 2.0±0.3 wt %. and anapproximate molecular weight of 500,000 grams per mole.

POLYSAR PB301 is a butyl rubber that has a Mooney viscosity (RPML 1+8 @125° C.) of 51±5 and an isoprene content of 1.75±0.2 mole %, and POLYSARCB1240 is a chlorinated butyl rubber that has a Mooney viscosity (RPML1+8 @ 125° C.) of 38±4 and a chlorine content of 1.25±0.1 wt %.

These polymers are all commercially available from Bayer, Inc., Sarnia,Ontario, Canada.

EXAMPLES Example 1

A blend of a polybutadiene which contained C—S—S—C bonds (BUNA CB24 fromBayer) and a brominated butyl rubber (POLYSAR BB2040 from Bayer) weremixed on a cool mill at 50° C. Blends of BUNA CB24 and a chlorinatedbutyl rubber (POLYSAR CB1240 from Bayer) and of BUNA CB 24 and anon-halogenated butyl rubber (POLYSAR PB301 from Bayer) were also mixedin a similar manner.

From samples of the blends there were prepared 5% solutions of theblends in hexane. These solutions were allowed to stand at roomtemperature and, after two hours, separation into two phases occurred,with the polybutadiene precipitated.

Other samples of the blends were mixed and heated for up to 25 minutesin a miniature internal mixer (Haake) equipped with a 75 ml capacityhead. The starting temperature was 130° C. and the speed was 60 rpm. Therubber temperature increased to 145° C. during the reaction.

The blend of BUNA CB24 and POLYSAR BB2040, after mixing from 5-15minutes in the Haake mixer, was dissolved in hexane. No significantseparation in the solution occurred over several days, indicatingsubstantial grafting between the polybutadiene and the brominated butylrubber. In contrast, solutions in hexane of the blends of BUNA CB24 andPOLYSAR CB1240, and of BUNA CB24 and POLYSAR PB301, did separate,indicating that the mixing in the Haake mixer had not caused graftingbetween the polybutadiene and the chlorinated butyl rubber ornon-halogenated butyl rubber.

Example 2

Blends of polybutadiene (BUNA CB24 or BUNA CB25; see Table 1 below) withbrominated butyl rubber (POLYSAR BB2040) were prepared in proportions30:70, 50:50 and 70:30. Each blend was subjected to mixing in a model BBanbury mixer. The starting temperature was 35° C. The blends were mixedfor the time periods specified in Table 1 below, during which time therubber temperature rose to 140-150° C. The temperatures of the graftedcopolymers when dumped from the Banbury mixer are given in Table 1.

Solutions of 5% polymer in hexane showed no significant separation onbeing held at room temperature for longer than 24 hours, indicating thatgrafting had occurred. The grafted polymers were then mixed with oil andingredients normally used in curing or vulcanizing, as follows:

Grafted polymer 100 Sundex 790 (processing oil) 10 Stearic acid 1.5 Zincoxide 3 Sulphur 1.4 CBS (N-cyclohexyl-2-benzo- 0.8 thiazole sulfenamide)

Samples of these were then cured at 170° C. in a moving die curerheometer (MDR). The optimum curing time, defined as t90+5 minutes, at170° C. was determined. Further samples were then cured for t90+5minutes at 170° C., and stress/strain properties were determined.Ungrafted blends of BUNA CB24 or BUNA CB25 and POLYSAR BB2040 were alsomixed with the same ingredients, cured in the same manner and theirstress/strain properties determined, to serve as controls. Results aregiven in Table 1 and are shown graphically in FIG. 1. It is clear thatall the compositions containing grafted copolymer show tensile strengthsuperior to the compositions containing ungrafted blends of polymers.

In Table 1:

column A gives results obtained when BUNA CB25 and POLYSAR BB2040 wereblended in equal proportions and mixed for 16 minutes to cause grafting.Results are also given for an ungrafted blend of BUNA CB25 and alsoPOLYSAR BB2040. The values obtained with the graft copolymer, divided bythe values obtained with the ungrafted blend and expressed as apercentage, are also given;

column B gives results obtained when BUNA CB24 and POLYSAR BB2040 wereblended in equal proportions and mixed for 16 minutes to cause grafting;

column C gives results obtained when BUNA CB25 and POLYSAR BB2040 wereblended in equal proportions and mixed for 7 minutes to cause grafting;

column D gives results obtained when 70 parts of BUNA CB25 and 30 partsof POLYSAR BB2040 were blended and mixed for 16 minutes to causegrafting. Results are also given for an ungrafted 70/30 blend of BUNACB25 and POLYSAR BB2040; and

column E gives results obtained when 30 parts of BUNA CB25 and 70 partsof POLYSAR BB2040 were blended and mixed for 17 minutes to causegrafting. Results are also given for an ungrafted 30/70 blend of BUNACB25 and POLYSAR BB2040.

TABLE 1 Column A Column B Column C Grafting time 0 16 16 7 (mins.)(Blend) Dump 147 147 147 Temperature (° C.) BUNA CB24 — — 50 — BUNA CB2550 50 — 50 Polysar BB2040 50 50 50 50 SUNDEX 790 10 10 10 10 StearicAcid 1.5 1.5 1.5 1.5 ZnO 3 3 3 3 S 1.4 1.4 1.4 1.4 CBS 0.8 0.8 0.8 0.8Strength Stress (G/B) % * (G/B) % * (G/B) % * Strain (t′₉₀ + 5 @ 170°C., die c.dumbells @ RT Hardness Shore A2 31 34 110 32 103 31 100 Inst.(pts) Ultimate Tensile 1.22 2.17 178 1.72 148 1.93 158 (MPa) UltimateElongation 335 330 99 280 84 365 109 (%) Stress @ 25 (MPa) 0.31 0.32 1030.35 113 0.32 103 Stress @ 50 (MPa) 0.47 0.51 109 0.52 111 0.51 109Stress @ 100 (MPa) 0.65 0.8 123 0.77 118 0.72 111 Stress @ 200 (MPa)0.91 1.38 152 1.18 130 1.09 120 Stress @ 300 (MPa) 1.27 1.8 142 1.51 119MDR Cure characteristics (1.7 Hz, 3° arc, 30 mins. @ 170° C.) MH (dN.m)29.48 28.11 95 28.05 95 29.1 99 ML (dN.m) 4.89 4.09 84 4.61 94 4.55 93t′ 90 (min) 15.41 16.48 107 16.47 107 16.09 104 Column D Column EGrafting time 0 16 0 17 (mins. ) (Blend) (Blend) Dump 150 143Temperature (° C.) BUNA CB24 — — — — BUNA CB25 70 70 30 30 PolysarBB2040 30 30 70 70 SUNDEX 790 10 10 10 10 Stearic Acid 1.5 1.5 1.5 1.5ZnO 3 3 3 3 S 1.4 1.4 1.4 1.4 CBS 0.8 0.8 0.8 0.8 Strength Stress (G/B)% * (G/B) % * Strain (t′₉₀ + 5 @ 170° C., die c.dumbells @ RT HardnessShore A2 34 32 94 29 30 103 Inst. (pts) Ultimate Tensile 1.49 2.09 1402.51 2.76 110 (MPa) Ultimate Elongation 3.85 260 68 565 445 79 (%)Stress @ 25 (MPa) 0.33 0.34 103 0.27 0.30 111 Stress @ 50 (MPa) 0.510.56 110 0.41 0.45 110 Stress @ 100 (MPa) 0.73 0.85 116 0.59 0.66 112Stress @ 200 (MPa) 1.02 1.44 141 0.87 1.10 126 Stress @ 300 (MPa) 1.322.09 158 1.17 1.64 140 MDR Cure characteristics (1.7 Hz, 3° arc, 30mins. @ 170° C.) MH (dN.m) 36 34.23 95 21.98 21.49 98 ML (dN.m) 5.044.83 96 4.75 4.15 87 t′ 90 (min) 19.16 19.24 100 12.23 13.11 107 *(property measured with Graft/property measured with Blend) × 100

Compositions similar to those whose properties are given in Table 1, butto which carbon black had been added as filler, were made and testedunder the same conditions as the compositions of Table 1. The resultsare given in Table 2 and shown graphically in FIG. 2.

In Table 2:

column A gives results obtained when BUNA CB25 and POLYSAR BB2040 wereblended in equal proportions and mixed for 18 minutes to cause grafting.Results are also given for an ungrafted blend of BUNA CB25 and POLYSARBB2040. The values obtained with the graft copolymer, divided by thevalues obtained with the ungrafted blend and expressed as a percentage,are also given;

column B gives results obtained when BUNA CB24 and POLYSAR BB2040 wereblended in equal proportions and mixed for 16 minutes to cause grafting;

column C gives results obtained when BUNA CB24 and POLYSAR BB2040 wereblended in equal proportions and mixed for 7 minutes to cause grafting;

column D gives results obtained when 70 parts of BUNA CB25 and 30 partsof POLYSAR BB2040 were blended and mixed for 16 minutes to causegrafting. Results are also given for an ungrafted 70/30 blend of BUNACB25 and POLYSAR BB2040; and

column E gives results obtained when 30 parts of BUNA CB25 and 70 partsof POLYSAR BB2040 were blended and mixed for 17 minutes to causegrafting. Results are also given for an ungrafted 30/70 blend of BUNACB25 and POLYSAR BB2040.

TABLE 2 Column A Column B Column C Grafting time 0 18 18 7 (mins.)(Blend) BUNA CB24 — — 50 — BUNA CB25 50 50 — 50 Polysar BB2040 50 50 5050 N-339 50 50 50 50 SUNDEX 790 10 10 10 10 Stearic Acid 1.5 1.5 1.5 1.5ZnO 3 3 3 3 S 1.4 1.4 1.4 1.4 CBS 0.8 0.8 0.8 0.8 Strength Stress (G/B)% * (G/B) % * (G/B) % * Strain (t′₉₀ + 5 @ 170° C., die c.dumbells @ RTCure Time (min) 21 21 21 20 Hardness Shore A2 60 60 100 58 97 60 100Inst. (pts) Ultimate Tensile 14.64 15.64 107 18.89 115 15.8 108 (MPa)Ultimate Elongation 400 380 95 430 108 415 104 (%) Stress @ 25 (MPa)1.03 1.02 99 1.01 98 1.07 104 Stress @ 50 (MPa) 1.43 1.49 104 1.41 991.48 103 Stress @ 100 (MPa) 2.31 2.59 112 2.45 106 2.39 103 Stress @ 200(MPa) 5.45 6.51 119 6.01 110 5.73 105 Stress @ 300 (MPa) 9.86 11.8 12010.82 110 10.32 105 MDR Cure characteristics (1.7 Hz, 3° arc, 30 mins. @170° C.) MH (dN.m) 37.78 39.68 105 40.27 107 38.4 102 ML (dN.m) 7.337.34 100 7.41 101 7.49 102 t′ 90 (min) 16.39 15.58 95 16.39 100 15.23 93Column D Column E Grafting time 0 16 0 17 (mins.) (Blend) (Blend) BUNACB24 — — — — BUNA CB25 70 70 30 30 Polysar BB2040 30 30 70 70 N-339 5050 50 50 SUNDEX 790 10 10 10 10 Stearic Acid 1.5 1.5 1.5 1.5 ZnO 3 3 3 3S 1.4 1.4 1.4 1.4 CBS 0.8 0.8 0.8 0.8 Strength Stress (G/B) % * (G/B)% * Strain (t′₉₀ + 5 @ 170° C., die c.dumbells @ RT Cure Time (min) 2323 19 19 Hardness Shore A2 58 58 100 60 63 105 Inst. (pts) UltimateTensile 16.76 15.21 81 15.17 14.43 95 (MPa) Ultimate Elongation 525 42080 430 370 86 (%) Stress @ 25 (MPa) 0.94 0.89 95 1.08 1.12 104 Stress @50 (MPa) 1.27 1.26 99 1.54 1.66 108 Stress @ 100 (MPa) 1.88 2.01 1072.62 3.05 116 Stress @ 200 (MPa) 3.88 5 130 6.03 7.32 121 Stress @ 300(MPa) 7.32 9.27 127 10.11 11.91 118 MDR Cure characteristics (1.7 Hz, 3°arc, 30 mins. @ 170° C.) MH (dN.m) 41.9 43.64 105 34.8 35.7 103 ML(dN.m) 7.5 7.6 101 7.13 7.09 99 t′ 90 (min) 16.01 18.24 101 14.44 14.3599 * (property measured with Graft/property measured with Blend) × 100

FIGS. 3, 4 and 5 show the change in glass transition temperature, Tg,with the graft copolymers whose results are given in Table 1. FIG. 3 isa graph of tan (δ) versus temperature for a 50/50 blend of a brominatedbutyl rubber (POLYSAR BB2040) and sulphurised polymer based onconjugated diolefin monomers (BUNA CB25) and for 50/50 grafts of POLYSARBB2040 with BUNA CB24 and BUNA CB25. Line 1 shows results obtained witha 50/50 mixture of POLYSAR BB2040 and BUNA CB25, grafted by mixing in aBanbury mixer for 16 minutes with a dump temperature of 147° C. Line 2shows results obtained with a 50/50 mixture of POLYSAR BB2040 and BUNACB24, grafted by mixing in a Banbury mixer for 16 minutes with a dumptemperature of 147° C. Line 3 shows the results obtained with a 50/50mixture of POLYSAR BB2040 and BUNA CB25, grafted by mixing in a Banburymixer for 7 minutes with a dump temperature of 140° C. Line 4 showsresults obtained with the ungrafted blend. The shift in peaks clearlyshows a shift in glass transition temperature, Tg, caused by grafting.

FIG. 4 is a graph of tan (δ) versus temperature for a 70/30 blend ofBUNA CB25 and POLYSAR BB2040 and also a graph for a 70/30 graft of BUNACB25 and POLYSAR BB2040 formed by mixing in a Banbury mixer for 16minutes with a dump temperature of 150° C.

FIG. 5 is a graph of tan (δ) versus temperature for a 30/70 blend ofBUNA CB25 and POLYSAR BB2040 and also a graph for a 70/30 graft of BUNACB25 and POLYSAR BB2040 formed by mixing in a Banbury mixer for 17minutes with a dump temperature of 143° C.

Example 3

Blends of polybutadiene (BUNA CB24) with (a) brominated butyl rubber(POLYSAR BB 2040), (b) chlorinated butyl rubber (POLYSAR CB1240) and (c)non-halogenated rubber (POLYSAR PB301) were premixed on a cool two rollmill at 40-50° C. The blends were then returned to the two roll mill andmixed at higher rubber temperatures ranging from 80 to 120° C. for 15 to60 minutes. The products were then dissolved in hexane. The blends withPOLYSAR CB1240 and POLYSAR PB301 separated within two hours, indicatingthat grafting had not occurred, whereas the blend with POLYSAR BB2040was slow to separate, indicating that grafting had occurred.

Example 4

50 parts polybutadiene (BUNA CB25) plus 50 parts brominated butyl rubber(POLYSAR BB2040), 5 parts polybutene (BP Chemicals; HYVIS 2000, Mol. Wt.5900), and 1 part Irganox 3052FF (Ciba) were mixed on a mill at toomtemperature. This blend was subsequently passed through a Berstorffcorotating intermeshing twin screw extruder ZE-25. This extruder has ascrew length of 1350 mm, and a diameter of 25 mm. Each pass typicallytook 2 to 3 minutes.

A number of reaction conditions were used as given in Table 3-5. Aqualitative measurement of grafting was obtained by measuring the amountof separated polymer after the reacted blend had been dissolved inhexane. The lower the separated polymer the slower the separation andthe greater the grafting.

TABLE 3 Rotation speed Barrel Extruder Separation (rpm) temperature (°C.) passes after 7 days Control 67.6 50 80 1 65.7 50 95 1 65.7 50 110 163.9 50 125 1 57.4 50 140 1 43.5 50 80 2 64.8 50 95 2 63.9 50 110 2 62.050 125 2 53.7 50 140 2 26.9

TABLE 4 Rotation speed Barrel Extruder Separation (rpm) temperature (°C.) passes after 7 days Control 70.8 50 125 1 66.7 50 125 2 63.3 50 1253 25 50 125 4 0 50 140 1 31.7 50 140 2 0 50 140 3 0 50 140 4 0 100  1401 53 100  140 2 0

Changes were made to the screw elements of the extruder with the resultsshown in Table 5.

TABLE 5 Rotation speed Barrel Extruder Separation (rpm) temperature (°C.) passes after 7 days Control 70.8 50 140 1 66.7 50 140 2 0 50 140 3 050 140 4 0

The data shown in tables 3-5 show that grafting was attained in the twinscrew extruder, particularly using barrel temperatures above 110° C.,and that increasing the residence time (increasing the number of passes)increased the degree of grafting

What is claimed is:
 1. A process for preparing a graft copolymer of abrominated butyl rubber and a polymer based on a conjugated diolefinmonomer comprising the steps of mixing solid brominated butyl rubberwith a solid polymer based on a conjugated diolefin monomer wherein thepolymer based on the conjugated diolefin monomer has C—S—(S)_(n)—Cbonds, wherein n is an integer from 1 to 7, and wherein the mixing iscarried out at a temperature greater than about 50° C. and for a timesufficient to cause grafting.
 2. A process according to claim 1 whereinthe mixing is carried out at a temperature in the range from 60° C. to180° C.
 3. A process according to claim 1 wherein the polymer based on aconjugated diolefin monomer is a polybutadiene.
 4. A process accordingto claim 1 wherein the polymer based on a conjugated diolefin monomer isa styrene-butadiene copolymer.
 5. A process according to claim 1 whereinfrom 90 to 10 parts by weight of the brominated butyl rubber are mixedwith from 10 to 90 parts by weight of the polymer based on a conjugateddiolefin monomer.
 6. A process according to claim 5 wherein from 70 to30 parts by weight of the brominated butyl rubber are mixed with from 30to 70 parts by weight of the polymer based on a conjugated diolefinmonomer.
 7. A process according to claim 1 wherein the mixing iseffected in an internal mixer.
 8. A process according to claim 1 whereinthe mixing is effected in an extruder.
 9. A process according to claim 1wherein the mixing is effected in part in an internal mixer and in partin an extruder.
 10. A process according to claim 1, further comprisingthe steps of admixing the graft copolymer prepared according to claim 1with a rubbery polymer selected from the group consisting of butadienerubbers, styrene-butadiene copolymers, styrene-isoprene-butadienecopolymers and styrene-isoprene-butadiene rubber, and mixing with carbonblack and vulcanizing agents, and curing to form a tire treadcomposition.
 11. A graft polymer formed by a process comprising thesteps of mixing solid brominated butyl rubber with a solid polymer basedon a conjugated diolefin monomer wherein the polymer based on theconjugated diolefin monomer has C—S—(S)_(n)—C bonds, wherein n is aninteger from 1 to 7, and wherein the mixing is carried out at atemperature greater than about 50° C. and for a time sufficient to causegrafting.
 12. A rubber composition containing a graft-polymer andoptionally one or more vulcanizing agents wherein the graft copolymer isformed by a process comprising the steps of mixing solid brominatedbutyl rubber with a solid polymer based on a conjugated diolefin monomerwherein the polymer based on the conjugated diolefin monomer hasC—S—(S)_(n)—C bonds, wherein n is an integer from 1 to 7, and whereinthe mixing is carried out at a temperature greater than about 50° C. andfor a time sufficient to cause grafting.
 13. A tire tread compositioncontaining a graft-polymer and optionally one or more vulcanizing agentswherein the graft copolymer is formed by a process comprising the stepsof mixing solid brominated butyl rubber with a solid polymer based on aconjugated diolefin monomer wherein the polymer based on the conjugateddiolefin monomer has C—S—(S)_(n)—C bonds, wherein n is an integer from 1to 7, and wherein the mixing is carried out at a temperature greaterthan about 50° C. and for a time sufficient to cause grafting.
 14. Arubber composition according to claim 12 wherein the rubber compositionis a vulcanized rubber.
 15. A rubber article containing a rubbercomposition wherein the rubber composition contains a graft-polymer andoptionally one or more vulcanizing agents wherein the graft copolymer isformed by a process comprising the steps of mixing solid brominatedbutyl rubber with a solid polymer based on a conjugated diolefin monomerwherein the polymer based on the conjugated diolefin monomer hasC—S—(S)_(n)—C bonds, wherein n is an integer from 1 to 7, and whereinthe mixing is carried out at a temperature greater than about 50° C. andfor a time sufficient to cause grafting.
 16. A rubber article accordingto claim 15 wherein said rubber article is a belt or roll.
 17. A rubberarticle according to claim 15 wherein said rubber article is a dampeningdevice.